Add a GPIO driver for the main GPIOs found in the TZ1090 (Comet) SoC.
This doesn't include low-power GPIOs as they're controlled separately
via the Powerdown Controller (PDC) registers.

The driver is instantiated by device tree and supports interrupts for
all GPIOs.

Changes in v4:
 - fix typos in DT bindings compatible properties
 - reference Documentation/devicetree/bindings/gpio/gpio.txt in
   gpio-ranges description in DT bindings
 - fix gpio-ranges examples in DT bindings (it must now have 3 cells)
 - gpio-tz1090: use of_property_read_u32 instead of of_get_property

Changes in v3:
 - separated from irq-imgpdc and removed arch/metag changes to allow
   these patches to go upstream separately via the pinctrl[/gpio] trees
   (particularly the pinctrl drivers depend on the new pinconf DT
   bindings).
 - some s/unsigned/unsigned int/.
 - some s/unsigned int/bool/ and use of BIT().
 - gpio-tz1090*: refer to <dt-bindings/gpio/gpio.h> and
   <dt-bindings/interrupt-controller/irq.h> flags in bindings.
 - gpio-tz1090*: move initcall from postcore to subsys.
 - gpio-tz1090: add REG_ prefix to some constants for consistency.
 - gpio-tz1090: add comment to explain tz1090_gpio_irq_next_edge
   cunningness.

Changes in v2:
 - gpio-tz1090: remove references to Linux flags in dt bindings
 - gpio-tz1090: make use of BIT() from linux/bitops.h
 - gpio-tz1090: make register accessors inline to match pinctrl
 - gpio-tz1090: update gpio-ranges to use 3 cells after recent ABI
   breakage
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Grant Likely <grant.likely@linaro.org>
Cc: Rob Herring <rob.herring@calxeda.com>
Cc: Rob Landley <rob@landley.net>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: linux-doc@vger.kernel.org
Cc: devicetree-discuss@lists.ozlabs.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>